Heat exchangers



United States Patent Inventors Harold John Coles Kenton, Harrow,England; Assignee Atomic Power Constructions Limited, Sutton, Surrey,England, a British company Appl. No. 779,898 Filed Nov. 29, 1968Patented Dec. 8, 1970 Priority Dec. 1, 1967 Great Britain No. 54900/67HEAT EXCHANGERS 4 Claims, 15 Drawing Figs.

US. Cl. 165/67. 122/510, 165/162, 165/163 Int. Cl. F281 9/00 Field ofSearch 165/ l 62, 67, 1631; 122/510 [56] References Cited UNITED STATESPATENTS 1,852,363, 4/1932 Parent 165/162 2,980,404 4/1961 Andersen et al165/ l 62X 3,286,767 1 l/ 1966 Evans 165/162X Primary Examiner-Albert W.Davis, Jr. Attorney-Holcombe, Wetherill & Brisebois ABSTRACT: A heatexchanger comprising helically wound tubes mounted upon a supportstructure comprising striplike support members apertured and slottedl atintervals along their length, and attachment members which are mountedupon the support members by entering arms on the attachment membersthrough the slots and sliding the former to a desired position on thesupport member. The attachment members have supporting surfaces .forreceiving the tubes and a boss which fits into an aperture intoanadjacent support member.

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1. HEAT'Excr ANGERs BACKGROUND To THE INvENIIoN I unit volume, such heatexchangers have found only limited application because the cost ofassembly is prohibitively high. The tubes must be supported to. maintainthem in a required,

.fixed relationship and it is known to use a support assembly comprisingthree support platesdisposed radially with respect to the axis of thehelically wound tubes. Each plate has a matrix of holes drilled in it atspaces corresponding to the helix lead and to thelateral spacing ofadjacent helices. The radially innermost tube helixi s fitted byrotating it axially and feeding its leading end in succession throughthe corresponding holes in the three support plates. A weld or someother mechanical lock is formed, at each hole, between tube and plate,and the process is repeated for each tube helix until the entire heatexchanger has been built up. Such a method is clearly extremelytime-consumingand therefore costly.

Similar problems arise in heat exchangers whose tubes are in otherconfigurations than helical although sometimes in a less acute form. w Iv e It is an object of the present invention to provide a constructionof heat exchanger which is easier and cheaper to assemble than theconstruction just described.

SUMMARY OF THE INVENTION A heat exchanger according to the inventioncomprises a plurality of tubes, a plurality of support members arrangedsubstantially transversely of the tubes and. a plurality of attachmentmembers securing the tubes to the support members, the tubes beingarranged in parallel layers with support members between adjacentlayers, and the attachment mem bers of one layer of tubes beingused tocarry the support members of the next adjacent layer of tubes.

The attachment members may comprise clips adapted to I secure one, twoor more adjacent tubes to the support.

The heat exchanger may comprise a plurality of tubes, a plurality ofsupport members, arranged substantially transversely of the tubes and aplurality of attachment members securing the tubes to the supportmembers. In one example of the invention the tubes are providedsubstantially in the form of helices.

The terrir helix is not used in a strictly mathematical sense but isintended to cover any generally helical configuration whether ofcircular transverse cross section or square, rectangular, elliptical orother shape. Moreover, a tube of helical form may be deliberatelydistorted in different directions at successive points of support alongits length, in order to induce position retaining stressing atthesupport points in order to derive a position retention force; suchsystems are described in greater'detail in copending application37398168.

The attachment membersmay consist of clips having one or w more curvedparts which engage thetube and a base part which is secured to thesupport member. The clip may be. of integral construction or the curvedpart or parts may be separate from the base part.

The or each curvedpartmay be resilient. Preferably, each clip is soformed that it has a surface for receiving a support memberof the nextadjacent group. For

' sembly, FIGS. 10, 11 and 12 are front,

example the support members may be strips apertured at regular intervalsin which case the clips may have bosses, a support The tubes may containfissile material in which case the heat exchanger becomes a fuel elementwhich may be helical. In this case heat is exchanged between the fissilematerial and coolant circulated past the tubes.

One method of assembling a heat exchanger embodying the inventioncomprises the steps of temporarily positioning a first group of supportmembers entering a first substantially helically wound tube over thefirst group, securing the first helix to the support members of thefirst group, positioning a second group of support members round andspaced from the first tube, entering a second substantially helicallywound tube over the second group, and securing the second tube to thesupport members of the second group.

According to thismethodthe heat exchanger is built outwards by startingat an innermost point, adding intermediate tubes and fixing theoutermost tubcfllast of all.

Alternatively, construction may proceed in an inward direction. Thefirst tube to be positioned would thus be the outermost one. This methodcomprises the steps of temporarily positioning a first group of supportmembers, entering a first substantially helically wound tube into thefirst group, securing the first tube to the support members of the firstgroup, entering a second group of support'members into the first helix,entering a second substantially helically wound tube into the secondgroup of support members, and securing the second tube to the supportmembers of the second group. 7

If a helixjntermediate between the inner and outer helixes is chosen asthe starting point, construction may be carried out by the use of bothmethods concurrently or sequentially. It should be noted that the choiceof construction method is not necessarily related to the type ofattachmentu'sed for fixing the tube to the support strip.

' BRIEFnEscRIPTIoN'oETIIE DRAWINGS FIG. 1 is an end view of a firstembodiment in diagrammatic form only, a 7

FIG. 2 is a section on the line'II-III of FIG. 1,

FIGS. 3 and 4 are front and side views respectively of part of a supportmember,

FIG. 5 is a section on the line V-V of FIG. 3,

FIGS. 6, 7 and 8 are top, side and front views respectively of anattachment member,

FIG. 9 is a side view of part of the: first embodiment after asplan andside views respectively of part of another-form of attachment member,

FIGS. 13, 14 are side and front views respectively of another part ofthe other form of attachment member, and

FIG. 15 is a side view of part of the second embodiment after assembly.1

DESCRIFIION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show an assembledheat exchanger in diagrammatic form only. The heat exchanger comprisesan outer cylindrical shell 1 and an inner cylindrical shell 2interconnected at their ends by three radial beams 3. The annulusdefined by the shells l, 2 contains a plurality of coaxial heli callywound tubes 4 each of whichis supported by a group of support memberseach comprising an elongated strip 5 suspended from the uppermost beams3. Each tube is attached to the support member of its supporting groupby attachment means not shown in FIGS. 1 and 2.

It should be noted that the various helically wound tubes may or may notbe interconnected, that they may be of differing lead, that is, helixangle, although the pitches are preferably the same, and they may or maynot extend the full length of the boilers. It is not necessary that thehelices should all be wound in the same direction. I

Referring first to FIGS. 3 4 and 5, each elongated support membercomprises along stainless steel strip 6 having holes 7 drilled throughit at regularly-spaced intervals. In section the strip is stepped alongeach long side as at 8 in FIG. 5 and the known as Nimonic 80A has curvedtube grips which extend from a central part 1 l which is slotted as at12, theends of the part being intume'd as at 13. The face of the clip isstepped as at 14 and has a central boss 15 beveled at 16 whose height isjust slightly less than the maximum thickness of strip 6.

To assemble the heat exchanger, the innermost helically wound tube isdealt with first. Three strips 6 are to be used to support the helix andthese strips are held temporarily in the positions they will occupy oncompletion of the entire assembly. The helix is'then slid down over thethree strips and temporarily supported in position. Tube support clipsare then engaged with the helix by springing the grips 10 over adjacentturns of the helix close to the point of attachment to the support plateand thenmounted upon the latter by passing the inturned ends 13 througha convenient slot 9 and sliding the clip along the strip until theattachment point is reached. This process is repeated until all theturns are clipped to each support plate every time they pass it. This isshown in FIG. 9 where adjacent turns 17, 18, 19 and 20 of the helix areclipped b'y clips 21 and 22 to a support strip 23.

t The three further support strips are now assembled by positioning themso that the bosses 15 of the clips already in position mate with theholes 7 of the further strips. The further support strips are nowattached, preferably by welding, to the bossesofthe innermost layer ofclips. The next innermost I j-xhelix is then slid over the three furthersupport strips and fixed to thela'tter by further clips. This is shownin FIG. 9. Adjacent turns of the next innermost helix are shown at 24,25 and 26 and are'clipped to support strip 27 by clips 28, 29 thesupport I strip 27 having been welded to the bosses of clips 21, 22 asindicated at 30.

The procedure is then repeated for each succeeding helix. FIG. 9 showsturns of two further helices 31, 32 secured by clips 33, 34 to supportstrips 35, 36 respectively.

' The inner shell is then inserted through the assembled helices, andthe outer shell positioned round the helices. The radialbeams are thenplaced in position and secured to the shells and to the support strips.

The attachment clip need not be of integral construction and analternative clip of two part construction will now be described.

The clip has a body part 37 shown in FIGS. 10, 11 and 12 having a slot38 and intumed ends 39. A boss 40 extends centrally from face 41 of thebody.

The grip portion of the clip is separate and is shown in FIGS. 13 and14. It comprises a metal sheet 42 bent into the form of a shallow U andhas a central hole 43.

clearance fit'between the clip body part 37 (or grips l0) and thesupport strip 44 in view of the risk of corrosion fretting occurring atthe contactin surfaces. One wa in which this may be achieved IS to welde body parts 37 or grips 10) to the support strips 44 at a number ofstaggered positions, and, at the remaining positions, todispense'entirely with the stirrup" connection to the adjacent strip.Thus, all. potential fretting is eliminated, and, by leavingoutsome ofthe interconnections and staggering the remainder, a support system isbuilt up which is flexible in the radial direction. This flexibility isdesirable to prevent excessive stress, due to thermal expansion, beinginduced in the tubes. Such stress might otherwise occur because thethermal expansion of the support members (having a temperature range ofroom temperature to primary heat transfer temperature) is greater thanthat of the tubes (which have a temperature range of room temperature tosecondary heat transfer temperature). The relative expansions of thetubes and support members will also depend on the ,difference betweenthe thermal properties of the materials from which they are constructed.I

The embodiments described above are vertically orientated, but theinvention is obviously applicable to any orientation; for example, iftheaxis was horizontal the tube support plates would either be considerablystrengthened, or would be supported intermediate their ends.

The tube clips illustrated both hold adjacent turns of a helix; clearlyeach turn could have a single clip, or more than two adjacent turnscould be supported by a single clip.

The invention has been described in relation to asystem in which theinnermost coil is. positioned first; given a large It will be understoodthat regularity of the lead and pitch of the helices is not essential.The support system can readily beadapted to support helices of irregularlead and pitch.

I claim:

1. A heat exchanger comprising in combination a first layer of tubes, afust series of support members of elongated form disposed transverselywith respect to the tubes of the first layer, first attachment membersmounted on the support members and carrying the tubes of the firstlayer, a second layer of tubes, a second series of support members'ofelongated form disposed transversely with respect to the tubes of thesecond layer, the support members of the second series Conveniently, thebody of the clip is of stainless steel whilst I positive jointingoperative has been performed up to this stage to assemble the two partclip.

The second row 46 of support strips is positioned by engaging the holestherein with the bosses 40. The bosses 40 are now welded to the secondsupport strips 46, this weld thus forms the dual function of attachingthe second support strips to the assembly, and of attaching to eachother the two parts of the clip. lt may be preferable, for example whenthe external heat transfer fluid is a reactor coolant gas, and for wherethe boiler is relatively inaccessible, to avoid the loose or beingcarried by the first attachnient members, second attachment membersmounted upon the support members of the second series and carrying thetubes of the second layer support members being of striplike form andhaving slots at spaced intervals along the length of the strip, and saidattachment members having inturned parts adapted to be entered throughsaid slots in order to mount the attachment members on the supportmember. s

2. A heat exchangeras claimed in claim 1 in which the support membersare apertured at spaced intervals along their length, and in which theattachment members have bosses which locate in the apertures to enablethe attachment'rnembers to carry support members.

3. A heat exchanger as claimed in claim 2 in which each attachmentmember consists of a curved part which engages a tube and a base part bywhich the attachment member is mounted upon a support member.

4. A heat exchanger as claimed in claim 2 in which each 'a't-f" tachmentmember consists of a first curved part which en-. gages a tube and asecond base part separate from the first part and by means of which theattachment member is mounted upon a support member.

